A satellite-derived re-analysis of surface-ocean pH variability in the coastal waters of India

Vase, Vinaya Kumar and Kumar, Rajan and Rahangdale, Shikha and Kartu, Sanjana and Solanki, Harshad and Jayasankar, J and Ratheesh Kumar, R and George, Grinson (2026) A satellite-derived re-analysis of surface-ocean pH variability in the coastal waters of India. Current Science, 130 (12). pp. 1077-1086. ISSN 0011-3891

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Abstract

Monitoring pH variations in coastal waters is essential for maintaining marine life and developing strategies to combat ocean acidification caused by climate change. The present study examines pH changes on interannual and seasonal scales along the northwest (NW), southwest (SW), southeast (SE), and northeast (NE) coasts of India over 30 years (1993–2022) using satellite data. Results reveal a significant decline in pH levels (R 2 = 0.727) across Indian coastal waters, with notable regional differences. The northeastern coast showed the greatest pH stability and the smallest decrease (R 2 = 0.798), while the southwestern coast experienced the highest variability (R 2 = 0.490). These regional pH fluctuations suggest varying resilience to ocean acidification. The NE and SW coasts, with higher variability, may be more susceptible to environmental changes, underscoring the importance of targeted monitoring and mitigation measures. In contrast, the more stable trends along the SE and NW coasts present opportunities to explore long-term resilience mechanisms. Seasonal fluctuations were evident everywhere, with winter consistently showing higher pH values and monsoon seasons the lowest. Principal component analysis indicated that the first two components accounted for 85.7% of the variance, highlighting factors such as seasonal river inflows, biological activity, and monsoonal freshwater input. Overall, these findings emphasise the importance of region-specific coastal management strategies to address climate change impacts and human pressures, while also providing a baseline for tracking future ocean acidification trends and assessing their effects on marine biodiversity and ecosystem services.

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